Polycarbonate polymers are excellent molding materials as products made therefrom have high impact strength, toughness, high transparency, wide temperature limits (high impact resistance below -60.degree. C. and a UL thermal endurance rating of 115.degree. C. with impact), good dimensional stability, high creep resistance and electrical properties which qualify it as sole support for current carrying parts.
Goldberg, U.S. Pat. No. 3,169,121, discloses a new class of resins comprising both carbonate and carboxylate groups in their linear chain possessing properties not obtainable in other polycarbonate resins. More specifically, the copolymer compositions of Goldberg, although possessing a wide range of desirable properties, are particularly outstanding in their high temperature strength properties, moldability and improved solvent resistance.
The copolyesters of Goldberg comprise recurring carbonate groups ##STR1## carboxylate groups ##STR2## and aromatic carbocyclic groups in the linear polymer chain, in which at least some of the carboxylate groups and at least some of the carbonate groups are bonded directly to ring carbon atoms of the aromatic carbocyclic groups. The copolyesters were prepared by reacting, as essential ingredients, a difunctional carboxylic acid, a dihydric phenol and a carbonate precursor.
It has also been proposed to make carbonate-carboxylate copolyesters by a modification of the technique suggested by Goldberg, and that is to phosgenate a solution of a dihydric phenol and certain low molecular weight polyesters. The products of such a process are random in nature in the sense that blocks of high molecular weight polycarbonates do not form. Moreover, the process itself is not amenable to large scale production and the number of polyester components suitable for use is limited because not all of them are soluble in the reaction solvent for phosgenation.
It has now been discovered that if a high molecular weight aromatic carbonate polymer resin is chemically modified by being segmented in a carbonate-carboxylate copolyester in which the major portion of the repeating units are aromatic polycarbonate blocks and the minor portion of the repeating units are blocks of a polyester or copolyester of a linear aliphatic dicarboxylic acid with one or more straight or branched chain dihydric aliphatic glycols and/or a polyether glycol, and optionally, an aromatic dibasic acid, such as isophthalic or terephthalic acid, then the resulting block carbonate-carboxylate copolyesters will have enhanced tear strength, compared to the aromatic polycarbonate resin itself. The improvement in tear strength and reduced notch sensitivity (in some instances) is achieved with minimal loss of other physical properties.
In particular, if certain aromatic, aliphatic, or partially aliphatic/aromatic, polyesters, or polyethers, are added to a reactor with a high molecular weight aromatic polycarbonate in the presence of a catalyst for ester interchange and heating is commenced under a high vacuum, there is caused a most desirable modification in the properties of the resulting aromatic polycarbonate molding resins.
By way of illustration, poly(neopentyl adipate), having a hydroxyl number in the range of 32 to 38, corresponding to a number average molecular weight of 3000 to 3500, is used as a source of blocks. This polyester is available from Ruco Division of Hooker Chemical Co., under the trade designation, Rucoflex 1016-35. The polyester is added to a reactor containing a reaction product of bisphenol-A and phosgene. A small amount of tetra (2-ethylhexyl)titanate catalyst is added. They are melted together under a slight vacuum. The vacuum is then increased to 0.1 mm Hg. and the temperature to 250.degree. C. After 30-60 minutes, the viscous melt is cooled to produce the product.
After forming the block carbonate-carboxylate copolyesters, alone, or combined with other thermoplastics into thin sheets or filsm, they are improved in tear strength and reduced in notched sensitivity as compared to films and sheets from unmodified aromatic polycarbonate. Other properties are improved as well. Many of the products are well-suited to injection molding and extrusion, as well.
The block carbonate-carboxylate copolyester products can also be converted to valuable modifications by adding reinforcements and/or fillers, such as glass fibers, talc, mica, clay and the like, or other conventional additives, such as flame retardants, pigments, etc.